Method of cold rolling coated sheet metal



Patented Nov. 3, 1936 Wired STATES PATENT OFFICE METHOD OF COLD ROLLING COATED SHEET METAL Jersey No Drawing. Application January 29, 1935, Serial No. 3,996

2 Claims. (01. 80-60) This invention pertains to a method of processing coated sheet metals. More particularly it relates to the processing of terne sheet or plate followingthe coating of the base metal with a lead- 5 tin or terne mixture. 1

Terne sheet or plate originally was intended only as a roofing material which usually, in light gages and small sizes, is known as short ternes. However, in recent years, heavy gage and large size sheetand plate have been terne coated and subjected to deep drawing operations resulting in gasoline tanks, automobile oil pans, caskets, etc., wherein the drawing characteristics of the base metal are aided by the terne coating which acts as a partial lubricant during the drawing opera- .tion. This grade, gage and size of sheet or plate is known as long ternes, to distinguish it from the short terne coated roofing material.

In addition to the need for uniform drawability there have been imposed severe surface requirements upon long ternes which have been diflicult to meet due partially to the soft nature of this lead-tin coating.

Demends for smoothness of surface, flatness and proper behavior upon forming or drawing, to-

gether with the difficulty of cold rolling or roller leveling long terne sheets after they have been coated, have heretofore caused such coldrolling and roller leveling operations to be performed prior to the coating operation.

However, due to the phenomena of aging characteristic of iron and steel products as intensified by the heat of the pot in the coating operation, the coated sheets upon subsequent forming and/or bendingjshow a tendency to give irregularly and locally which produces objectionable characteristics called fluting. If the same material is subjected to stamping or drawing (rather than bending or forming) the irregularfiow of 40 metal produces so-called stretcher strains. This tendency of the terne-coated sheet-like metal to flue or stretcher strain is traceable to the internal straining of the crystalline structure of the base metal during the coating operation.

Very severe and repeated cold rolling or roller leveling operations prior to coating will stiffen the sheets to a point where the heating of the pot will not bring back the full tendency of the sheets to flute or stretcher strain, but such excessive work on the sheets prior to coating is costly} and it also injures the ductility of the sheets, thus rendering them less suited for difiicult forming or drawing operations.

This fluting and straining could be reduced somewhat by roller leveling after coating, providing that the sheets were formed or stamped shortly thereafter for otherwise with time the eiiects of such roller leveling are soon lost.

A more substantial remedy for this tendency of 5 the coated sheets to flute and stretcher strain is .to cold roll such sheets after coating. If the proper amount of elongation is imposed on such coated sheets by such cold rolling the tendency to flute and stretcher strain is completely elimi- 1o.

nated and the tendency for this conditionto return is greatly delayed as compared to the rapid return of such tendencies after a mere roller leveling operation.

However, the coated sheets upon being thus 15 cold rolled would slip and slide about between the rolls (due to the slippery nature of the coating) as to twist, camber or bow the sheets and cause the terne coating to take on a streaky appearance. The soft, slippery coating was readily susceptible 0 to marking by the rolls and any loose particles thereon pitted the sheet almost instantaneously.

This was particularly true of the excess coating upon the rear end of the sheets so coated, commonly known as list end. This list end metal 25 would leave the sheets and stick to the rolls, thus badly marking all subsequent sheets. V

The slippage of these coated sheets when cold rolled was further accentuated by the presence of palm oil which as part of the coating procedure 30,

was not entirely removed in the cleaning of the coated metal in a so-called branning machine. Thus it was practically impossible to cold roll terne coated sheets to eliminate the tendency toward fluting and stretcher straining without in- 35 curring prohibitive damage to the sheets.

One of the objects of our invention is a practical method of cold rolling terne coated sheet metal surface finish.

A further object is a method of cold rolling terne coated sheet metal with no slippageof the sheets between the rolls and to the exclusion of cambered edges, such cold rolling taking place 55 without the necessity for removing all traces of oil from the surfaces of the coated sheet.

The above and other objects become more apparent to those skilled in the art from the reading 5 of the following specification and claims.

In carrying out our invention the base metal is hot rolled to gage in any convenient manner, such as strip or sheet, and thereafter properly heat treated to produce the physical properties desired for satisfactory stamping, pressing or otherwise forming the metal in the manufacture of shaped articles.

After heat treating the base metal strip or sheet it is preferably processed to provide flatness by providing a single cold roll pass or its equivalent as contrasted to the excessive cold working heretofore. necessary.

The resulting sheet, after said cold rolled pass, has the desired ductility, surface and flatnessand the thus processed sheet is then preferably pickled, and then coated with a mixture of lead and tin to form terne sheets or plates in the usual manner. After the sheets are coated they are cleansed by passing through the usual branning machine, which removes the major and all excess palm oil deposited during the terne coating operation. Those skilled in the art will readily recognize that some traces of palm oil remain on coated sheets after they have passed through the branning machine, however, these traces of palm oil are not too detrimental to the processing of this invention, although they were detrimental in the processing methods of the prior art.

During the coating process, which is a hot process, there is a tendency to cause the base metal to stretcher strain or flute when worked such as by drawing or forming operations, and this tendency must be removed or eliminated in 40 order to provide satisfactory coated sheets for subsequent stamping, pressing or drawing. In order to remove the strains set up as a result of the coating process thecoated sheets are cold rolled on a wet cold rolling mill. A we mill,

which is well known in the art, comprises a set of rolls which are constantly flooded with a liquid, such as water, oil, or a combination of water and oil, so that the sheets passing through between said rolls are; actually processed-or rolled with a film of water between each side of the sheet and the rolls. In other words, the pressure on the rolls is delivered to the sheets being processed through liquid 'films.

Heretofore attempts have been made to cold' roll terne coated sheets in dry cold rolling mills,

however, the terne coated sheets had such a slippery surface as to make such rolling very diflicult and in some cases almost impossible, and furthermore the slipping or moving o'f'the sheetsrelative to the roll when adry mill is used marked and -destroyed the-surface of the sheets. The art has long understood that wet mills always have a lubricating effect and, recognizing the inherent slipperiness of terne coating, failed, as far'as is known, to use the wet type ofmill for cold rolling terne coated sheets in the belief that slippage would be aggravated.

sheet and said mill.

We have discovered that by using a wet mill on terne coated sheets which have been cleaned only in the branning machine so that the sheets still retain traces of palm oil we can cold roll such terne coated sheets with excellent and improved results.

We. have discovered terne coated sheets rolled on a Wet mill permits as great a reduction as is desired and necessary to remove the stretcher strains and fluting resulting from the heat of the terne coating, with little or no pressure, and in extreme cases with an average maximum pressure necessary to result in a 2 per cent or 3 per cent elongation. The rolling under liquid produces a uniform surface finish of the terne coated sheets which may vary from a bright surface resulting from the use of smooth rolls to a surface terne coat silver frosting resulting from the use of rough rolls. In the use of certain mills for this type of processing the rolls are usually turned as truly cylindrical as possible and the blanket of liquid prevents dirt and dust from settling upon the rolls and the sheets being processed, thus resulting in a final sheet having an extremely smooth surface free from pits, dents, scratches and the like. The extremely soft nature of the terne coating makes it extremely important to prevent the deposit of any foreign particles on the surface during the rolling operation or on the rolls with which the sheet is processed in order to prevent the marring of the surface.

We have discovered further that by the use ofa wet mill the liquid layer covering the rolls prevents any particles of excess metal on the list or tail end of the sheet from leaving the sheet from adhering to the rolls, thus marring the surface of the sheet. Heretofore it has been diflicult to prevent metal particles from leaving the sheet and adhering to the rolls of a dry cold rolling mill when rolling terne coated sheets.

Wehave also discovered that by the use of a wet mill, contrary to all expectations and teachings in the art, the terne coated sheets do not slip or slide in the mill and, therefore, marring of the surfaces from this cause is prevented.

While we have described a certain'speciflc embodiment of our invention it will be understood that we do not wish to be limited thereto, since various modifications may be made within the scope of the appended claims.

Weclaimi 1. The method which includes rolling ternecoated sheets and plates in a cold wet mill wheresheet in a cold'mill to reduce the tendency of said sheet toward the development of said strains, and applying a liquid to the rolls of said cold mill to minimize slippage between said terne-coated LEWIS W. BEALE. JosEP E. MURPHY. 

